1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD panel driving circuit. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for reducing the size of the panel driving circuit as well as increasing the reliability of the device.
2. Discussion of the Related Art
An LCD is a display device utilizing transmissivity changes that occur when an electric field is applied to a liquid crystal material. In general, each pixel of a color LCD panel consists of three liquid crystal cells having a delta arrangement. Each cell outputs one of the video signals corresponding to R(red), G(green), and B(Blue). For a black and white display, the cells have a stripe arrangement. When those pixels are arranged in a matrix of rows and columns to form a display panel, a character signal or an image signal is outputted according to a control signal from the driving circuit.
As illustrated in FIGS. 1 and 2, 6-bit R, G, B digital video signals, a vertical synchronizing signal, V-SYNC, and a horizontal synchronizing signal, H-SYNC, for generating a cell driving signal of the LCD panel are inputted from a VGA chip to a timing control circuit 110. A digital video signal from the timing control circuit 110 is then applied to each column driver 120. A cell driving signal is applied to each row driver 130.
The timing control circuit 110 of the conventional LCD panel driving circuit controls the output timing of the digital video signal and transmits a cell driving signal to the row driver 130.
FIG. 2 illustrates the column driver 120 of the conventional LCD panel driving circuit shown in FIG. 1. The column driver 120 includes a shift block 121 for sequentially applying the video signal output from the timing control circuit 110 to a digital-to-analog (D/A) converter block 122. The D/A converter block 122 converts the digital video signal into an analog video signal. A gamma correction circuit 125 corrects the non-linear distortion of the video signal. A sample/hold circuit 123 outputs an analog video signal converted by the D/A converter block 122, and a buffer 124 applies an output from the sample/hold circuit 123 to each cell of the LCD panel.
In addition, a plurality of bus lines are required to apply the 6-bit digital video signals for transmission from the shift block 121 to the D/A converter block 122 of the low column driver 120. A plurality of signal transmission lines apply the converted analog video signal of the D/A converter block 122 to the buffer 124 through the sample/hold circuit 123.
The operation of the conventional LCD panel driving circuit as aforementioned will be described with reference to FIGS. 1 and 2.
If the digital video signal and the vertical/horizontal synchronizing signals V/H-SYNC are inputted to the timing control circuit 110, the timing control circuit 110 determines the output timing of the video signal input, transmits it to the column driver 120, and transmits the cell driving signal based on the vertical/horizontal synchronizing signals V/H-SYNC signals V/H-SYNC to the row driver 130.
The digital video signal is then applied to D/A converters in the D/A converter block 122 by the control of the shift block 121 in the column driver 120 of FIG. 2.
If a first data block of the digital video signal is inputted to the shift block 121, the signal is applied to the first three D/A converters D/A1, D/A2, D/A3 of the D/A converter block 122 to perform analog conversion. If a second data block is inputted, the signal is transmitted to D/A converters D/A4, D/A5, D/A6 of the D/A converter block 122 to convert the signal until all channels in the column driver 120 are converted. A converted analog video signal is then applied to each cell of the LCD panel 140 through the sample/hold circuit 123 and the buffer 124 to operate the LCD panel 140.
The conventional LCD panel driving circuit having the D/A converter block 122 in every column driver 120 requires an 18 bit-bus line in order to transmit 6-bit R, G, B digital video signals from the timing control circuit 110 to the column driver 120.
Therefore, each column driver 120 needs the D/A converter block 122 which increases the size of the circuit and also its power consumption. Moreover, since more bus lines are required to transmit the video signal between the timing control circuit 110 and the column driver 120, circuit malfunction caused by electromagnetic interference is a common problem. The entire size of the LCD panel driving circuit is thus increased and it takes more time to design the circuit. As a result, the cost per product is greatly increased.